1. Field of the Disclosure
The present disclosure relates to a flat panel display device, and more particularly, a liquid crystal display device with a built-in touch screen, which facilitates enhanced driving performance, and reduced manufacturing cost by simplifying the manufacturing process, and a method for manufacturing the same.
2. Discussion of the Related Art
According to development of various mobile electronic equipment, such as mobile terminals and notebook computers, there is increasing demand for a suitable flat panel display device. The flat panel display device may include an active-matrix liquid crystal display device (LCD), a plasma display panel (PDP), a field emission display device (FED), or a light-emitting diode display device (LED), etc. Among the various flat panel display devices, the LCD device is widely used owing to various advantages, for example, development maturity for mass production, ease of driving, low power consumption, high-quality resolution, and large screen size.
Instead of a related art mouse or keyboard used as an input device to the mobile electronic equipment, a touch screen has been recently used as an input device in conjunction with a flat panel display device, wherein the touch screen enables a user to directly input information by the use of a finger, pen, or stylus.
The touch screen has been widely applied in various fields, for example, mobile terminals for navigation, terminals for industrial use, notebook computers, automatic teller machines (ATM), mobile phones, MP3 players, personal digital assistants (PDA), portable media players (PMP), Play Station Portables (PSP), mobile game machines, digital media broadcasting (DMB) receivers, and tablet personal computers (PC). Touch screens have also been integrated into non-mobile electric appliances such as refrigerators, microwave ovens, and laundry machines. Furthermore, the easy operational method of the touch screen rapidly enlarges the field for applications.
For reducing size of the mobile electronic equipment, an LCD device with a built-in touch screen has been researched and developed. An in-cell touch type LCD device has been developed, wherein the in-cell touch type LCD device refers to an LCD device which uses an element existing in the active structure, for example, a common electrode on a lower substrate, as a touch-sensing electrode.
FIG. 1 illustrates an LCD device with a built-in touch screen 10 according to the related art. Referring to FIG. 1, the LCD device with a built-in touch screen 10 according to the related art comprises lower and upper substrates 50 and 60, respectively, bonded to each other with a liquid crystal layer (not shown) interposed in between.
As an example of built-in touch screen operation, the pixel array 40 can also be used as a touch screen TS sensor. A small voltage may be applied to the pixel array 40 to create a uniform electrostatic field. When a conductor, such as a human finger or other object, touches the uncoated front surface, a capacitor Ctc is formed. A controller connected to the touch screen TS sensor can determine the location of the touch indirectly from the change in the capacitance as measured from the four corners of the touch screen TS sensor.
On the upper substrate 60, there are a black matrix 62; red, green, and blue color filters 64R, 64G, and 64B; and an overcoat layer 66. In this case, the black matrix 62 defines a pixel region corresponding to each of a plurality of pixels. Also, the red, green, and blue color filters 64R, 64G, and 64B are respectively formed in the respective pixel regions defined by the black matrix 62. The overcoat layer 66 covers the red, green, and blue color filters 64R, 64G, and 64B and the black matrix 62 to planarize the upper substrate 60.
On the lower substrate 50, there is a pixel array 40 including a plurality of pixels to drive the liquid crystal layer and detect a touching point. Each of the pixels is defined by gate lines and data lines which cross each other. At the crossing portion of the gate lines and data lines there is a thin film transistor (‘TFT’) for each pixel. Each of the pixels also includes a common electrode and a pixel electrode.
FIG. 2 is a cross sectional view illustrating a lower substrate 50 in the LCD device with a built-in touch screen according to the related art. FIG. 2 shows a lower substrate in a fringe field switch (FFS) mode, which is described in further detail below.
Referring to FIG. 2, each pixel of the lower substrate 50 is formed on a glass substrate 80. Each pixel includes a light-shielding layer 71 to prevent incident light reaching the active layer 72; a buffer layer 51 on the light-shielding layer 71; an active layer 72 on the buffer layer 51; a gate insulating layer 52 on the active layer 72; and a gate electrode 73 of a metal material on the gate insulating layer 52, wherein the gate electrode 73 is partially overlapped with the active layer 72 in that at least a portion of the gate 73 is over some of the active layer 72. Also included are an interlayer dielectric (ILD) 53 and a data electrode (source/drain) 74. The interlayer dielectric 53 is formed on the gate electrode 73, to insulate the gate electrode 73 from the data electrode (source/drain) 74. The data electrode 74 is electrically connected to the active layer 72.
Further, a first contact hole is formed by etching the gate insulating layer 52 and the interlayer dielectric 53, wherein the contact hole exposes a predetermined portion of the active layer 72. The data electrode 74 is formed by burying a metal material in the contact hole to contact the active layer 72. The active layer 72, the gate insulating layer 52, the gate electrode 73, and the data electrode 74 form portions of the TFT.
In each pixel of the lower substrate 50, there are a first passivation layer (PAS0) 54, a second passivation layer (PAS1) 55, a common electrode 75, a conductive line (3rd metal) 76, a third passivation layer (PAS2) 56, and a pixel electrode 77, which are sequentially formed on the interlayer dielectric 53. The first and second passivation layers (PAS0, PAS1) 54 and 55 are formed to cover the gate electrode 73 and the data electrode 74. The common electrode 75 is formed on the second passivation layer 55, wherein the common electrode 75 is formed of a transparent conductive material such as Indium-Tin-Oxide (ITO). The conductive line 76 is formed on and electrically connected with a predetermined portion of the common electrode 75. The third passivation layer 56 is formed to cover the common electrode 75 and the conductive line 76. The pixel electrode 77 is electrically connected with an upper portion of the third passivation layer 56 and the data electrode 74, wherein the pixel electrode 77 is formed of a transparent conductive material such as ITO.
A second contact hole is formed by partially etching the first, second and third passivation layers (PAS0, PAS1, and PAS2) 54, 55 and 56. After etching, the upper portion of the data electrode 74 is exposed via the second contact hole. The pixel electrode 77 is formed inside the second contact hole formed by etching the first, second, and third passivation layers (PAS0, PAS1, PAS2) 54, 55 and 56, whereby the pixel electrode 77 is electrically connected with the data electrode 74.
Herein, the TFT serving as a switching element of the LCD device may be formed in a top gate structure or bottom gate structure. In case of the TFT with the top gate structure, light emitted from the backlight unit is applied to the active layer 72 through the substrate 80, whereby a light leakage current occurs in the active layer 72, and degradation such as crosstalk may arise. Crosstalk is an undesirable visual phenomenon resulting from unintended pixels turning on to image misinformation. The combination of residual gate voltage during the decay time after the gate is turned off plus photonic energy absorbed from the backlight unit may be enough to at least partially turn the TFT on when it is intended to be off.
To prevent such limitations, a metal layer, i.e., the light-shielding layer 71 for shielding light is disposed under the active layer 72. Therefore, light of the backlight is prevented from being irradiated on the active layer 72, and thus leakage current is minimized.
The electron mobility property of amorphous silicon limits the operational speed and the geometric design rules of the TFT. To overcome such limitations, low temperature poly-silicon (LTPS) is being used as a material for forming the active elements (for example, TFT) of the lower substrate 50 because the electron mobility is about 100 times higher than a-Si. Even when LTPS is used as a material for forming the TFT of the lower substrate 50, as shown in FIG. 3, ten (10) masks corresponding to patterned layers are used in a manufacture process, and therefore, a plurality of detailed processes (for example, 155 steps) are performed.
LTPS enables higher resolution display panels as compared to a-Si, and has excellent characteristic for TFT operations. However, LTPS requires the manufacture process to have more masks and detailed processes than a-Si because there are extra annealing steps. Therefore, the price competitiveness is limited and manufacturing efficiency is reduced.